Process for breaking petroleum emulsions



Patented Jan. 27, 1953 PROCESS FOR BREAKING PETROLEUM EMULSIONS Melvin De Groote, University City, Mo assignor to Petrolite Corporation, a corporation of Delaware No Drawing. Application May 14, 1951, Serial No. 226,318

11 Glaims.

This invention relates to petroleum emulsions of the water-in-oil type that are commonly referred' to as cut oil, roily oil, emulsified oil, etc., and which comprise fine droplets of naturally-occurring waters or brines dispersed in a more or less permanent state throughout the oil which constitutes the continuous phase of the emulsion.

One object of my invention is to provide a novel process for breaking or resolving emulsions of the kind referred to. Another object of my invention is to provide an economical and rapid process for separating emulsions which have been preparedunder controlled conditions from mineral oil, such as crude oil and relatively soft waters or weak brines. Controlled emulsification and subsequent demulsification under the conditions just mentioned are of significant value in removing impurities, particularly inorganic salts from pipeline oil.

Demulsification as contemplated in the present application includes the preventive step of commingling the demulsifier with the aqueous component which would or might subsequently become either phase of the emulsion, in absence of such precautionary measure. Similarly, such demulsifier may be mixed with the hydrocarbon component.

The present invention is concerned with a process for breaking petroleum emulsions by means of an ester obtained by reaction between (a) a polycarboxy acid and (b) an oxypropylated liquid polyamide resin. One such resin which is employed is formed by the reaction of the dimerized and trimerized unsaturated acids of vegetable oils, or similar oils, with ethylene diamine. The resin as produced commercially is ofa dark amber color and is available as a viscous liquid. As is well known, these resins are obtained by reacting the polymeric fatty acids with diamines, particularly alkylene diamines, in which the nitrogen atoms are separated by not more than 8 carbon atoms as in the case of ethylene diamine, propylene diamine, butylene diamine, phenylene diamine, cyclohexylene diamine, etc. Hexylene diamine and octylene diamine are also satisfactory. The dimerization and trimerization of fatty acids is well known and described in various patents. See, for example, U. S. Patent No. 2,450,332, dated Septem- 1.

her 28, 1948, to De Groote.

More specifically, the present invention is concerned with a process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters which are those of (A) a polycarboxy acid with (B) high molal oxypropylation derivatives of liquid polyamide resins. The polyamide resins are those obtained from an alkylene diamine having not more than 8 carbon atoms and fatty acid polymers obtained by the polymerization of unsaturated fatty acids to a stage not beyond trimerization. These polyamide resins have a molecular weight between 2500 and 15,000. The high molal oxypropylation derivatives thereof are obtained by subjecting them to reaction with propylene oxide, giving a product having a molecular weight between 5000 and 65,000, and in which the liquid polyamide resin represents not more than 50% by weight, these weights and proportions being on a statistical basis and on the assumption of complete reaction. The oxypropylated product is xylene-soluble. In forming the esters one mole of polycarboxy acid is used for each available hydroxyl radical of the oxypropylene resin.

The preparation of polyamide resins is well known and possibly is best exemplified by ma terials such as nylon. However, comparable resins, and more particularly liquid resins, derived from polymerized fatty materials are Well known and have been described in various pubmately 10,000. These particular resins are made from fatty acids obtained from vegetable 0115. Similar resins have been prepared from fatty acids obtained from unsaturated marine oils, In these instances the molecular Weights appear to be somewhat higher and this is true, also, i. e., an increased molecular weight when diamine other than ethylene diamine is used. Any comparable resin may be employed provided that (a) it is a liquid and (b) that it is reasonably close to the above molecular weight range, for instance, 2,500 to 12,000 or 15,000. On the other hand, if one starts with a dimerized fatty acid having a molecular weight of about 575 or thereabouts, and reacts two moles of such material for example with 2 moles of ethylene diamine so as to produce polyamide, it is possible that the lower molecular weight limit is in the neighborhood of 1,000.

Having obtained or prepared a suitable polyamide resin of the kind described, such resin is then reacted with two to ten times its weight of propylene oxide, in presence of a suitable catalyst, which may be either an alkaline catalyst such as caustic soda, sodium methylate, or the like, or an acidic catalyst such as stannic chloride. For obvious reasons I prefer to use an alkaline catalyst. My preference is to use caustic soda, or sodium hydroxide.

As will be pointed out hereinafter, for a number of reasons it is very difiicult to arrive at the molecular weight of the oxypropylated product even if the molecular weight of the initial resin were known accurately, which is usually not the case. Stated another way, there is difficulty in determining the exact molecular weight of the initial resin and even greater difiiculty in determining the molecular weight of the oxypropylated derivative. The best means of designation seems to be to describe the product in terms of manufacture as exemplified by the hereto attached claims. Certain high molal oxypropylation products have been reacted with polycarboxy acids to produce acidic fractional esters which are useful in the resolution of petroleum emulsions. For example, reference is made to copending application of C. M. Blair, Serial No. 70,811 filed January 13, 1949 (now Patent 2,562,878, granted August 7, 1951) in which there is described, among other things, a process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of an esterification product of a dicarboxylic acid and a polyalkylene glycol in which the ratio of equivalents of polybasic acid to equivalents of polyalkylene glycol is in the range of 0.5 to 2.0, in which the alkylene group has from 2 to 3 carbon atoms, and in which the molecular weight of the product is between 1,500 to 4,000.

Similarly, reference is made to U. S. Patent No. 2,499,365 dated March '7, 1950, to De Groote and Keiser. See Examples 795 and 80b of said aforementioned De Groote and Keiser patent. In these instances polymeric fatty acid ethylene diamine resins were treated with several times their weight of ethylene oxide.

Reference is made also to U. S. Patent No. 2,454,544 dated November 23, 1948, to Bock and Rainey.

I wish to point out, however, that the present invention is differentiated from the invention of the aforementioned Bock and Rainey patent in numerous ways and particularly the following: (A) As the initial raw material I employ a fatty acid polyamide resin and not a phenol-formaldehyde resin; (B) although in said invention apparently an ethylene oxide, propylene oxide, or butylene oxide can be used I have found only propylene oxide to be satisfactory in the instant process; (C) in the aforementioned Book and Rainey patent the products described are neutral salts obtained by neutralization with an alkaline hydroxide equivalent, but in the instant invention neutralization destroys the effectiveness of the demulsifying agent and the product must not be neutralized; and (D) the products described in said aforementioned Book and Rainey patent appear to be invariably and inevitably detergents and are characterized by having detergent properties. These detergent properties are imparted wholly in all likelihood, or at least to a marked degree, by the neutralization step previously indicated. However, the instant materials when examined for detersive properties appear to be substantially devoid of any detersive properties. The method of examination is described in Synthetic Detergents, Mc- Cutcheon, MacNair-Dorland Company, New York, 1950.

Complementary to the aspect of the invention herein disclosed is my companion invention concerned with the new chemical products or compounds used as the demulsifying agents in the processes or procedures of this invention, as well as the application of such chemical compounds, products, or the like, in various other arts and industries, along with the method for manufacturing said new chemical products or compounds which are of outstanding value in demulsification. See my co-pending application, Serial No. 226,319, filed May 14, 1951.

For convenience, what is said hereinafter will be divided into four parts:

Part 1 is concerned with the preparation of the oxypropylated derivatives previously referred to;

Part 2 is concerned with the preparation of the acidic esters by reacting the oxypropylated derivatives with polycarboxy acids;

Part 3 is concerned with the use of the acidic fractional esters as demulsifiers for resolving petroleum emulsions of the water-in-oil type, and

Part 4 is concerned with derivatives valuable for various purposes, including demulsification but not specifically claimed in the instant application.

PART 1 For a number of well known reasons equipment, whether laboratory size, semi-pilot plant size, pilot plant size, or large scale size, is not as a rule designed for a particular alkylene oxide. Invariably and inevitably, however, or particularly in the case of laboratory equipment and pilot plant size the design is such as to use any of the customarily available alkylene oxides, i. e., ethylene oxide, propylene oxide, butylene oxide, glycide, epichlorohydrin, styrene oxide, etc. In the subsequent description of the equipment it becomes obvious that'it is adapted for oxyethylation as well as oxypropylation.

Oxypropylations are conducted under a Wide variety of conditions, not only in regard to presence or absence of catalyst, and the kind of catalyst, but also in regard to the time of reaction.

temperature-of reaction, speed of reaction, pressure during reaction, etc. For instance, oxyalkylations can be conducted at temperatures up to approximately 200 C. with pressures in about the same range up to about 200 pounds per square inch. They can be conducted also at temperatures approximating the boiling point of water or slightly above, as for example to C. Under such circumstances the pressure will be less than 30 pounds per square inch unless some special procedure is employed as is sometimes the case, to wit, keeping an atmosphere of inert gas such as nitrogen in the vessel during the reaction. Such low-temperature-low reaction rate oxypropylations have been described very completely in U. S. Patent No. 2,448,664, to H. R. Fife, et al., dated September 7, 1948. Low temperature, low pressure oxypropylations are particularly desirable where the compound being subjected to oxypropylation contains one, two or three points of reaction only, such as monohydric alcohols, glycols and triols.

Since low pressure-low temperature-low reaction speed oxypropylations require considerable time, for instance, 1 to 7 days of 24 hours each to complete the reaction they are conducted as a rulewhether on a laboratory scale, pilot plant scale, or large scale, so as to operate automatically. The prior figure of seven days applies especially to large-scale operations. I have used conventional equipment with two added automatic features; (a) a solenoid controlled valve which shuts off the propylene oxide in event that the temperature gets outside a predetermined and set range, for instance, 95 to 120 C., and (b) another solenoid valve 'which shuts 01f the propylene oxide (or for that matter ethylene oxide if it is being used) if the pressure gets beyond a predetermined range, such as 25 to pounds. Otherwise, the equipment is substantially the same as is commonly employed for this purpose where the pressure of reaction is higher, speed of reaction is higher, and time of reaction is much shorter. In such instances such automatic controls are not necessarily used.

Thus, in preparing the various examples I have found it particularly advantageous to use labora tory equipment or pilot plant which is designed to permit continuous oxyalkylation whether it be oxypropylation 0r oxyethylation. With certain obvious changes the equipment can be used to permit oxyalkylation involving the use of glycide where no pressure is involved except the vapor pressure of a solvent, if any, which may have been used as a diluent.

As previously pointed out the method of using propylene oxide is the same as ethylene oxide. This point is emphasized only for the reason that the apparatus is so designed and constructed as to use either oxide.

The oxypropylation procedure employed in the preparation of the oxyalkylated derivatives has been uniformly the same, particularly in light of the fact that a continuous automatically-controlled procedure was employed. In this procedure the autoclave was a conventional autoclave made of stainless steel and having a capacity of approximately 15 gallons and a working pressure of one thousand pounds gauge pressure. This pressure obviously is far beyond any requirement as far as propylene oxide goes unless there is a reaction of explosive violence involved due to accident. The autoclave was equipped with the conventional devices and openings, such as the variable-speed stirrer perating at speeds from 50 R. P. M. to 560 R. P. M.; thermometer well and thermocouple for mechanical thermometer; emptying outlet; pressure gauge, manual vent line; charge hole for initial reactants; at least one connection for introducing the alkylene oxide, such as propylene oxide or ethylene oxide, to the bottom of the autoclave; along with suitable devices for both cooling and heating the autoclave, such as a cooling jacket, and, preferably, coils in addition thereto, with the jacket so arranged that it is suitable for heating with steam or cooling with water and further equipped with electrical heating devices. Such autoclaves are, of course, in essence small-scale replicas of the usual conventional autoclave used in oxyallrylation procedures. In some instances in exploratory preparations an autoclave having a smaller capacity, for

instance, approximately 3 /2 liters in one case and about 1% gallons in another case, was used.

Continuous operation, or substantially continuous operation, was achieved by the use of a separate container to hold the alklene oxide being employed, particularly propylene oxide. In conjunction with the smaller autoclaves, the container consists essentially of a laboratory bomb having a capacity of about one-half gallon, or somewhat in excess thereof. In some instances a larger bomb was used, to wit, one having a capacity of about one gallon. This bomb was equipped, also, with an inlet for charging, and an eductor tube going to the bottom of the container so as to permit discharging of alkylene oxide in the liquid phase to the autoclave. A bomb having a capacity of about 60 pounds was used in connection with the 15-gallon autoclave. Other conventional equipment consists, of course, of the rupture disc, pressure gauge, sight feed glass, thermometer, connection for nitrogen for pressuring bomb, etc. The bomb was placed on a scale during use. The connections between the bomb and the autoclave were flexible stainless steel hose or tubing so that continuous Weighings could be made without breaking or making any connections. This applies also to the nitrogen line, which was used to pressure the bomb reservoir. To the extent that it was required, any other usual conventional procedure or addition which provided greater safety was used, of course, such as safety glass protective screens, etc.

Attention is directed again to what has been said previously in regard to automatic controls which shut off the propylene oxide in event temperature of reaction passes out of the predetermined range or if pressure in the autoclave passes out of predetermined range.

With this particular arrangement practically all oxypropylations become uniform in that the reaction temperature was held within a few degrees of any selected point, for instance, if C. was selected as the operating temperature the maximum point would be at the most C. or 112 (3., and the lower point would be 95 or possibly 98 C. Similarly, the pressure was held at approximately 30 pounds maximum within a 5- pound variation one way or the other, but might drop to practically zero, especially where no solvent such as xylene is employed. The speed of reaction was comparatively slow under such conditions as compared with oxyalkylations at 200 C. Numerous reactions were conducted in which the time varied from several hours up to 48 hours for completion of the final member of the series. However, in the particular series hereinafter recorded in detail the reaction took place in considerably less time, in fact, the entire oxypropylation took less than 24 hours. The minimum time recorded was approximately one hour. Reactions indicated as being complete in 5 and 6 hours ordinarily may have been complete in a lesser period of time in light of the automatic equipment employed. This applies also where the reactions were completed in a shorter period of time, 4 to 5 /2 hours. In the addition of propylene oxide, in the autoclave equipment as far as possible the valves were set so all the propylene oxide if fed continuously would be added at a rate so that the predetermined amount would, react within the first 5 hours of the 6-hour period, or two-thirds of any shorterperiod. This meant that if the reaction was interrupted automatically for a period of time for pressure to drop or temperature to drop the predetermined amount of oxide would still be added in most instances well within the predetermined time period. Sometimes where the addition was a comparatively small amount in a -hour period there would be an unquestionable speeding up of the reaction by simply repeating the examples and using 1, 2, or 3 hours instead of 4 to 5 hours.

When operating at a comparatively high temperature, for instance, between 150 to 200 C., an unreacted alkylene oxide such as propylene oxide, makes its presence felt in the increase in pressure or the consistency of a higher pressure. However, at a low enough temperature it may happen that the propylene oxide goes in as a liquid. If so, and if it remains unreacted there is, of course, an inherent danger and appropriate steps must be taken to safeguard against this possibility; if need be a sample must be withdrawn and examined for unreacted propylene oxide. One obvious procedure, of course, is to oxypropylate at a modestly higher temperature, for instance, at 140 to 150 C. Unreacted oxide affects determination of the acetyl or hydroxyl value of the hydroxylated compound obtained.

The higher the molecular weight of .the compound, i. e., towards the latter stages of reaction, the longer the time required to add a given amount of oxide. One possible explanation is that the molecule, being larger, the opportunity for random reaction is decreased. Inversely, the lower the molecular weight the faster the reaction takes place. For this reason, sometimes at least, increasing the concentration of the catalyst does not appreciably speed up the reaction,

particularly when the product subjected to oxy alkylation has a comparatively high molecular weight. However, as has been pointed out previously, operating at a low pressure and a low temperature even in large scale operations as much as a Week or ten days time may lapse to obtain some of the higher molecular Weight derivatives from monohydric or dihydric materials.

In a number of operations the counterbalance scale or dial scale holding the propylene oxide bomb was so set that when the predetermined amount of propylene oxide had passed into the reaction the scale movement through a time opcrating device was set for either one to two hours so that reaction continued for 1 to 3 hours after the final addition of the last propylene oxide and thereafter the operation was shut down. This particular device is particularly suitable for use on larger equipment than laboratory size autoclaves, to wit, on semi-pilot plant or pilot plant size, as well as on large scale size. This final stirring period is intended to avoid the presence of unreacted oxide.

In this sort of operation, of course, the temperature range was controlled automatically by either use of cooling water, steam, or electrical heat, so as to raise or lower the temperature. The pressuring of the propylene oxide into the reaction vessel was also automatic insofar that the feed stream was set for a slow continuous run which was shut oiT in case the pressure passed a predetermined point as previously set out. All the points of design, construction, etc., were conventional including the gauges, check valves and entire equipment. As far as I am aware at least two firms, and possibly three,

specialize in autoclave equipment such as I have employed in the laboratory, and are prepared to furnish equipment of this same kind. Similarly ilot plant equipment is available. This point is simply made as a precaution in the direction of safety. Oxyalkylations, particularly involving ethylene oxide, glycide, propylene oxide, etc., should not be conducted except in equipment specifically designed for the purpose.

Example 1a.

The starting material employed was a polyamide resin of the kind previously referred to and sold commercially by General Mills, Inc., Minneapolis, Minnesota, under the name of Polyamide Resin No. 94. The catalyst employed was caustic soda. The autoclave used was one having a capacity of about 15 gallons or approximately pounds. The equipment had all the control devices previously described. The speed of the stirrer could be varied from 150 to 350 R. P. M.

19.5 pounds of polyamide resin (General Mills No. 94) were charged into the autoclave. To this there was added one pound of caustic soda. The reaction pot was flushed out with nitrogen, the autoclave was sealed and the automatic devices adjusted for injecting 44.0 pounds of propylene oxide in about a 5 /2 hour period. This time period was comparatively short due in part to the fact that there was present a considerable amount of catalyst. This particular oxypropylation was conducted at a temperature of 125 to C. The pressure regulator was set for 35-37 pounds per square inch. Since the propylene oxide reacted rather rapidly, at no time did the pressure rise above 33 pounds per square inch and it is probable the bull: of the reaction took place at a lower pressure. The initial introduction of the propylene oxide was not started until the heating devices had raised the temperature well above the boiling point of water, for instance, close to 120 C. As pointed out previously the reaction was complete in what was a relatively short period of time. At the end of the reaction part of the reaction mass was withdrawn as a sample and the remainder subjected to further oxypropylation as described in Example 2a, immediately following.

Example 2a 48.50 pounds of the reaction mass previously identified as Example 101., and equivalent to 14.62 pounds of the polyamide resin, 33.13 pounds of propylene oxide and .75 pound of caustic soda, were reacted with 42 pounds of propylene oxide. The conditions of reaction as far as temperature and pressure were concerned were identical with Example 1a, preceding. This statement applies also to the next two oxypropylations, to wit, Examples 3a and 4a. The time requiredwas slightly less than in Example la, about 4 hours. At the completion of the reaction part of the reaction mass was withdrawn and the remainder subjected to further oxypropylation as described in Example 3a, immediately following.

Example 3a See what has been said previously in regard to conditions of reaction as far as temperatureand pressure are concerned. The time period was comparatively short, just one hour. At the end of the reaction part of the sample was with- 9 drawn and the remainder subjected to a final oxypropylation step as described in Example 4a, following.

Example 4a 70 pounds of the reaction mass identified as Example 3a, immediately preceding, and equivalent to 8.85 pounds of the polyamide resin, 60.7 pounds of propylene oxide, and .45 pound of caustic soda, were subjected to reaction with '11 pounds of propylene oxide in the manner previously described. As to conditions of reaction as far as temperature and pressure are concerned, see the preceding examples. The time required to add the oxide was 4 hours.

What has been said preceding is presented in tabular form in Table 1, following, with some added information as to molecular weight and as to solubility of the reaction product in water, xylene, and kerosene.

10 course, would be the same if sodium methylate had been used.

Speaking of insolubility in water or solubility in kerosene such solubility test can be made simply by shaking small amounts of the mate-- rials in a test tube with water, for instance, using 1% to 5% approximately based on the amount of water present.

PART 2 As previously pointed out the present invention is concerned with acidic esters obtained from the oxypro'pylated derivatives described in Part 1, immediately preceding, and polyoarboxy acids, particularly tricarboxy acids like citric and dicarboxy acids such as adipic acid, phthalic acid, or anhydride, succinic acid, diglycollic acid, sebacic acid, azelaic acid, aconitic acid, maleic acid or anhydride, citraconic acid or anhydride, maleic acid or anhydride adducts as obtained by TABLE 1 Composition Before Composition at End Max Max EX. Pres. Time No. Amide Oxide Amide Oxide Cata- 3 O S lbs. hrs.

Amt Amt, 3 Amt, Amt, lyst, g sq. in.

lbs lbs. lbs lbs. lbs. lbs.

1a 19. 5 1.0 3, 580 19. 5 44. 1.0 650 125-130 35-37 2u 14. 62 33. 13 75 6, 750 14. 62 75. 13 75 705 125-130 35-37 1 3L 9. 8 50. 42 50 8, 640 9. 80 G7. 5 700 125-130 -37 l 41. 8. 85 60. 70 10, 020 8. 85 71. 45 898 125-130 35-37 4 Example 1a. was soluble in water but insoluble in both xylene and kerosene; Examples 2a, 3a and 4a were all emulsifiable in water, soluble in xylene but insoluble in kerosene.

As is well known, there is no satisfactory way of determining molecular weight of many polymeric resins, or even simpler compounds, in some instances where the molecular weight is above 2,000. In fact, it has been estimated that polyarm'de resins of the kind previously described vary from 3,000 to 10,000, and that the range probably includes 2,500 and also up to 15,000. The reactivity of the hydrogen atoms attached to nitrogen in such complex molecule is only partially understood. In other words, there is a question as to whether the labile hydrogen atoms other than those attached toterminal nitrogen atoms react with propylene oxide in the incipient stage of the reaction. There is some evidence that they do, at least in the latter stages. The question also arises as to what extent such labile hydrogen atoms are susceptible to determination by the usual methods of determining hydro-xyl value or modifications thereof. In the above table the values given are on the assumption that all hydrogen atoms attached to nitrogen are reactive. The ratio has been marked equivalent. Its significance is -questionable. The only satisfactory description resides in the molal ratios of propylene oxide to polyamide and these are the ratios which are the basis for the theoretical molecular weight.

In any event, the preceding directions can be followed readily to produce products of the kind previously described and which are suitable for forming esters as pointed out in Part 2, following.

The final products varied from an amber to reddish amber in color, to somewhat viscous fluids of a slightly pale amber color in one or two instances. This was more or less the characteristic of all the oxypropylated products at the various stages. These products were, of course, slightly alkaline due to the residual caustic soda. The residual basicity, due to the catalyst, of

the Diels-Alder reaction from products such as maleic anhydride, and cyclopentadiene. Such acids should be heat stable so they are not decomposed during esterification. They may contain as many as 36 carbon atoms as, for example, the acids obtained by dimerization of unsaturated fatty acids, unsaturated monocarboxy fatty acids, or unsaturated monoca-rb xy acids having 18 carbon atoms. Reference to the acid in the hereto appended claims obviously includes the anhydrides or any other obvious equivalents. My preference, however, is to use polycarboxy acids having not over 8 carbon atoms.

The production of esters including acid esters (fractional esters) from polycarboxy acids and glycols or other hydroxylated compounds is well known. Needless to say, various compounds may be used such as the low molal ester, the anhydride, the acyl chloride, etc. However, for purpose of economy it is customary to use either the acid or the anhydride. A conventional procedure is employed. On a laboratory scale one can employ a resin pot of the kind described in U. S. Patent No. 2,499,370, dated March 7, 1950 to De Groote and Keiser, and particularly with one more opening to permit the use of a porous spreader i-f hydrochloric acid gas is to be used as a catalyst. Such device or absorption spreador consists of minute alundum thimbles which are connected to a glass tube. One can add a sulfonic acid such as paratoluene sulfonic acid as a catalyst. There is some objection to this because in some instances there is some evidence that this acid catalyst tends to decompose or rearrange the oxypropylated compounds, and particularly likely to do so if the esterification temperature is too high. In the case of polycarboxy acids such as diglycollic acid, which is strongly acidic there is no need to add any catalyst. The use of hydrochloric acid gas has one advantage over paratoluene sulfonic acid and that'is thatat the end of the reaction it can be removed by flushing out with nitrogen, whereas there is no reasonably convenient means available of removing the paratoluene sulfonic acid or other sulfonic acid employed. If hydrochloric acid is employed one need only pass the gas through at an exceedingly slow rate so as to keep the reaction mass acidic. Only a trace of acid need be present. I have employed hydrochloric acid gas or the aqueous acid itself to eliminate the initial basic material. My preference, however, is to use no catalyst whatsoever.

The products obtained in Part 1 preceding may contain a basic catalyst. As a general procedure I have added an amount of half-concentrated hydrochloric acid considerably in excess of what is required to neutralize the residual catalyst. The mixture is shaken thoroughly and allowed to stand overnight. It is then filtered and refluxed with the xylene present until the water can be separated in a phase-separating trap. As soon as the product is substantially free from water the distillation stops. This preliminary step can be carried out in the flask to be used for esterification. If there is any further deposition of sodium chloride during the reflux stage needless to say a second filtration may be required. In any event the neutral or slightly acidic solution of the oxypropylated derivatives described in Part 1 is then diluted further with sufiicient xylene, decalin, petroleum solvent, or

centrated hydrochloric acid to just neutralize the residual basic catalyst. To this product one can then add a small amount of anhydrous sodium sulfate (sufiicient in quantity to take up any water that is present) and then subject the mass to centrifugal force so as to eliminate the hydrated sodium sulfate and probably the sodium chloride formed. The clear, somewhat viscous straw-colored or dark ambler liquid so obtained may contain a small amount of sodium sulfate or sodium chloride but, in any event, is perfectly acceptable for esterification in the manner described.

There may be a trace of a basic amine radical remainin and to such an extent a salt can be formed. However, this should cause no difiiculty in the various instances where I have used polyamide resins as a starting material.

It is to be pointed out that the products here described are not polyesters in the sense that there is a plurality of both oxypropylated polyamide resin radicals and acid radicals; the product is characterized by having only one oxyproylated polyamide resin radical.

The data included in the subsequent tables, 1. e., Tables 2 and 3, are self-explanatory and very complete and it is believed no further elaboration is needed.

TABLE 2 Mol. Amt. f Ex. Theo. Wt. g Poly N 010i No. of M W droxyl Actual Based Hyd Polycarboxy Reactant carhoxy Acid Cm d of V of H. V. on C d React- Ester p H. C H 0 Actual 2;? ant H. V (grs la 3, 550 15. 7 86. 6 650 192 Diglycolic Acid 39.6 141 ,580 15. 7 86.6 650 195 Aconitic Acid. 52. 2 la 3, 580 15.7 86.6 650 196 016111: Acid 38.0 10 3, 580 15. 7 86. 6 650 200 Maleic Anhydrld a0. 2 1a 3, 580 15. 7 86. 6 650 199 Phthalic Anhydride 45. 9 in 3,580 15. 7 86. 6 650 196 oimiconic Anhyd s3. 7 2a 6, 750 s. 34 79.9 705 19s Diglycolic Acid. s7. 6 2a 6. 750 s. 34 79. 9 705 19s Oxalic Acid. s5. 4 211 6,750 8.34 79.9 705 205 AconiticAcld 50.5 2a 6, 750 8. 34 79. 9 705 210 Maleic Anhydrid 29. 2 2a 6, 750 s. 34 79.9 705 201 Phthalic Anhydride.. 42. 2 2a 6, 750 8.34 79.0 705 200 Oitraconic Anhydride 31.3 3L1 8,640 6.51 71.2 790 202 Diglycolic Acid 34.3 36 8,640 6.51 71.2 790 202 Aconitic Ac1d. 44.5 3a 8, 640 6. 51 71. 2 700 196 Oxalic Acid. :41. 2 '55 8,640 6.51 71.2 790 206 Phthalic Anhydridc 38.6 311 8.640 6.51 71.2 790 217 Maleic Anhydride 27.0 311 8, 640 6.51 71.2 790 199 Citraconic Anhydride... 28.2 401 10,020 5.6 62.6 898 200 Diglycolic Acid 30.0 411 10,020 5. 6 62. 6 898 200 Aconitic Acid 38. 8 4a 10, 020 5. 6 62. 6 898 21s Oxalic Acid a0. 6 4a 10, 020 5. 6 62. 6 898 206 Maleic Anhydride 22. 4 4c 10, 020 5. 6 62. 6 592 206 P11012111; Anhydride. s4. 0 4a 10, 020 5. 6 62. 6 898 232 Citraconic Anhyd 29. O

the like, so that one has obtained approximately TABLE 3 a solution. To this solution there is added a. polycarboxylated reactant as previously (16- Ex. N0.0f S Amt s m W 1 olvent Solvent t fiat fiCL. mgr scribed, such as phthallc anhydride, succlmc acid Afld Ester (gm) a 3% ff 0111v (cc) or anhydride, diglycollic acid, etc. The mixture is refluxed until esterification is complete as in- 22-; dicated by elimination of water or drop in carboxyl value. Needless to say, if one produces 230 a. half-ester from an anhydride such as phthahc anhydride, no water is eliminated. However, if it is obtained from diglycollic acid, for example, 5 145 water is eliminated. All such procedures were conventional and have been so thoroughly de- 232 145 scribed in the literature that further consideration will be limited to a few examples and a 21 139 comprehensive table. 33 112 4 Other procedures for eliminating the basic 27 145 residual catalyst, if any, can be employed. For if; example, the oxyalkylation can be conducted in absence of a solvent or the solvent removed after 240 176 oxypropylation. Such oxypropylation end prod- 261 144 not can then be acidified with just enough conl The procedure for manufacturing the esters has been illustrated by preceding examples. If for any reason reaction does not take place in a manner that is acceptable, attention should be directed to the following details: (a) Recheck the hydroxyl or acetyl value of the oxypropylated primary amines of the kind specified and use a stoichiometrically equivalent amount of acid; (b) if the reaction does not proceed with reasonable speed either raise the temperature indicated or else extend the period of time up to 12 or 16 hours if need be; (c) if necessary, use of paratoluene sulfonic acid or some other acid as a catalyst; (42) if the esterification does not produce a clear product a check should be made to see if an inorganic salt such as sodium chloride or sodium sulfate is not precipitating cut. Such salt should be eliminated, at least for exploration experimentation, and can be removed by filtering. Everything else being equal as the size of the molecule increases and the reactive hydroxyl radical represents a smaller fraction of the entire molecule, more difiiculty is involved in obtaining complete esterification.

Even under the most carefully controlled condition of oxypropylation involving comparatively low temperatures and long time of reaction there are formed certain compounds whose compositions is still obscure. Such side reaction products can contribute a substantial proportion of the final cogeneric reaction mixture. Various su e tio s h e made as to the nature of these compounds, such as b ing cyclic polymers of p opy x d dehydration products with the appearance of a vinyl radical, or isomers of propylene oxide or derivatives thereof, 1. e., of an aldehyde, ketone, or allyl alcohol. In some instances an attempt to react the ,stoichiometric amount of a polycarboxy acid with the oxypropylated derivative results in an excess of the car-boxylated reactant for the reason that apparently under conditions of reaction less reactive hydroxyl radicals are present than indicated by the hydroxyl value. Under such circumstances there is simply a residue of the carboxylic reactant which can be removed by filtration or, if desired, the esterification procedure can be repeated using an appropriately reduced ratio of carboxylic reactant.

Even the determination of the hydroxyl value by conventional procedure leaves much to be desired due either to the cogeneric materials previously referred to, or for that matter, the presence of any inorganic salts or propylene oxide. Obviously this oxide should be eliminated.

The solvent employed, if any, can be removed from the finished ester by distillation and particularly vacuum distillation. This is especially true when xylene has been used as in the previous examples. The appearance of the final productsare somewhat the same as prior to esterification, usually amber or reddish-amber, or even dark reddish amber, in color. Unless there is some reason to do otherwise it is my preference to handle these esters as 50% solutions in suitable solvents. They can be bleached with bleaching clays, filteringchars and the like. However, for the purpose of demulsification or thelike color is nota factor and decolorization is not justified.

PART 3 Conventional demulsifying agents employed in the treatment of oil field emulsions are used as such, or after dilution with any suitable solvent, such as water, ,petroleumhydrocarbons, such as benzene, toluene, xylene, tar acid oi}, cresol, anthracene oil, etc. Alcohols, particularly aliphatic alcohols, such as methyl alcohol, ethyl ,alcohol, denatured alcohol, propyl alcohol, butyl alcohol, hexyl alcohol, oc-tyl alcohol, etc., may be employed as diluents. Miscellaneous solvents such as pine oil, carbon tetrachloride, sulfur dioxide extract obtained in the refining of petroleum, etc., may be employed as diluents. Similarly, the material or materials employed as the demulsifying agent of my process may be admixed with one or more of the solvents customarily used in connection with conventional demulsifying agents. Moreover, said material or materials may be used alone or in admixture with other suitable wellknown classes of demulsifying agents.

It is well known that conventional demulsifying agents may be used .in a water-soluble form, or in an oil-soluble form, or in a form exhibiting both oiland water-solubility. Sometimes they may be used in a form which exhibits relatively limited oil-solubility. However, since such reagents are frequently used in a ratio of 1 to 10,000 or 1 to 20,000, or 1 to 30,000, or even 1 to 40,000, or 1 to 50,000 as in desalting practice, such an apparent insolubility in oil and water is not significant because said reagents undoubtedly have solubility within such concentrations. This same fact is true in regard to the material or materials employed as the demulsifying agent of my process.

In practicing my process for resolving petroleum emulsions of the water-in-oil type, a treating agent or demulsifying agent of the kind above described is brought into contact with or caused to act upon the emulsion to be treated, in any of the various apparatus now generally used to resolve or break petroleum emulsions with a chemical reagent, the above procedure being used alone or in combination with other demulsifying procedure, such as the electrical dehydration process.

One type of procedure is to accumulate a volume of emulsified oil in a tank and conduct a batch treatment type of demulsification procedure to recover clean oil. In this rocedure the emulsion is admixed with the demulsifier, for example by agitating the tank of emulsion and slowly dripping demulsifier into the emulsion. In some cases mixing is achieved by heating the emulsion while dripping in the demulsifier, depending upon the convection currents in the emulsion to produce satisfactory admixture. In a third modification of this type of treatment, a circulating pump withdraws emulsion from, e. g., the bottom of the tank, and reintroduces it into the top of the tank, the demulsifier being added, for example, at the suction side of said circulating P p.

In a second type of treating procedure, the demulsifier is introduced into the well fluids at the well-head or at some point between the wellhead and the final oil storage tank, by means of an adjustable proportioning mechanism or proportioning pump. Ordinarily the flow of fluids through the subsequent lines and fittings suffices to produce the desired degree of mixing of demulsifier and emulsion, although in some instances additional mixing devices may be introduced into the fiow system. In this general procedure, the system may include various mechanical devices for withdrawing free water, separating-entrained water, or accomplishing quiscent settling of the chemica-lized emulsion. Heating 15 devices may likewise be incorporated in any of the treating procedures described herein.

A third type of application (down-the-hole) of demulsifier to emulsion is to introduce the demulsifier either periodically or continuously in diluted or undiluted form into the well and to allow it to come to the surface with the well fluids, and then to flow the chemicalized emulsion through any desirable surface equipment, such as employed in the other treating procedures. This particular type of application is decidedh useful when the demulsifier is used in connection with acidification of cacareous oil-bearin strata, especially if suspended in or dissolved in the acid employed for acidification.

In all cases, it will be apparent from the foregoing description, the broad process consists simply in introducing a relatively small proportion of demulsifier into a relatively large proportion of emulsion, admixing the chemical and emulsion either through natural flow or through special apparatus, with or without the application of heat, and allowing the mixture to stand quiescent until the undesirable water content of the emulsion separates and settles from the mass.

The following is a typical installation.

A reservoir to hold the demulsifier of the kind described (diluted or undiluted) is placed at the well-head where the efiluent liquids leave the well. This reservoir or container, which may vary from gallons to 50 gallons for convenience, .is connected to a proportioning pump which injects the demulsifier drop-wise into the fluids leaving the well. Such chemicalized fluids pass through the flowline into a settling tank. The settling tank consists of a tank of any convenient size, for instance, one which will hold amounts of fluid produced in 4 to 24 hours (500 barrels to 2000 barrels capacity), and in which there is a perpendicular conduit from the top of the tank to almost the very bottom so as to permit the incoming fluids to pass from the top of the settling tank to the bottom, so that such incomin fluids do not dis turb stratification which takes place during the course of demulsiflcation. The settling tank has two outlets, one bein below the water level to drain on the water resulting from demulsiflcation or accompanying the emulsion as free water, the other being an oil outlet at the top to permit the passage of dehydrated oil to a second tank, being a storage tank, which holds pipeline or dehydrated oil. If desired, the conduit or pipe which serves to carry the fluids from the well to the settling tank may include a section of pipe with bafiles to serve as a mixer, to insure thorough distribution of the demulsifier throughout the fluids, or a heater for raising the temperature of the fluids to some convenient temperature, for instance, 120 to 160 F., or both heater and mixer.

Demulsification procedure is started by simply setting the pump so as to feed a comparatively large ratio of demulsifier, for instance, 1:5,000. As soon as a complete break or satisfactory demulsification is obtai. ed, the pump is regulated until experience shows that the amount of demulsifier being added is just sufficient to produce clean or dehydrated oil. The amount being fed at such stage is usually 1:10,000, 1215, 000, 1 :20,000, or the like.

In many instances the oxyalkylated products herein specified as demulsiflers can be conveniently used without dilution. However, as previously noted, they may be diluted as desired with any suitable solvent. For instance, by mixing 75 parts by weight of the product of Example 7b,

with 15 parts by weight of xylene and 10 parts by weight of isopropyl alcohol, an excellent demulsifier is obtained. Selection of the solvent will vary, depending upon the solubility characteristics of the oxyalkylated product, and of course will be dictated in part by economic considerations, i. e., cost.

As noted above, the products herein described may be used not only in diluted form, but also may be used admixed with some other chemical demulsifier. A mixture which illustrates such combination is the following:

Oxyalkylated derivative, for example, the prodnot of Example 7b, 20%;

A cyclohexylamine salt of a polypropylated napthalene monosulfonic acid, 24%;

An ammonium salt of a polypropylated napthalene monosulfonic acid, 24%;

A sodium salt of oil-soluble mahogany petroleum sulfonic acid, 12%;

A high-boiling aromatic petroleum solvent, 15;

Isopropyl alcohol, 5

The above proportions are all weigh-t percents.

PART 4 As pointed out previously the final product obtained is a fractional ester having free carboxyl radicals. Such product can be used as an intermediate for conversion into other derivatives which are effective for various purposes, such as the breaking of petroleum emulsions of the kind herein described. For instance, such product can be neutralized with an amine so as to increase its water-solubility such as triethanolamine, tripropanolamine, oxyethylated triethanolamine, etc. Similarly, such product can be neutralized with some amine which tends to reduce the watersolub-ility such as cyclohexylamine, benzylamine, decylamine, tetradecylamine, octadecylamine, etc. Furthermore, the residual carboxyl radicals can be esterified with alcohols, such as low molal alcohols, methyl, ethyl, propyl, butyl, etc., and also high molal alcohols, such as octyl, decyl, cyclohexanol, benzyl alcohol, octadecyl alcohol, etc. Such products are also valuable for a variety of purposes due to their modified solubility. This is particularly true where surface-active materials are of value and especially in demulsification of water-in-oil emulsion.

Having thus described my invention, what I claim as new and desire to secure by Letters Paten is:

1. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a polycarboxy acid, and (B) high molal oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and higher fatty acid polymers obtained by the polymerization of unsaturated fatty acids to a stage not beyond trimerization; (b) the molecular weight range of the initial liquid polyamide resin be within 2,500 to 15,000; (0) the molecular weight of the oxypropylation end-product be within the range of 5,000 to 65,000 on an average statistical basis; ((1) the oxypropylation endproduct be xylene-soluble; (e) the xylene solu bility characteristics of the oxypropylation endproduct be substantially the result of the oxypropylation step;

resin represent (1) the initial liquid polyamide not more than 50% by weight of basis; and that the preceding provisos be based on complete reaction involving the propylene oxide and the initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the polycarboxy acid for each available hydroxyl radical.

2. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a polycarboxy acid, and (B) high mola1 oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and dimerized higher fatty acids; (b) the molecular weight range of the initial liquid polyamide resin be within 2,500 to 15,000; the molecular weight of the oxypropylation end-product be within the range of 5,000 to 65,000 on an average statistical basis; (01) the oxypropylation endproduct be xylene-soluble; (e) the xylene solubility characteristics of the oxypropylation endproduct be substantially the result of the oxypropylation step; (1) the initial liquid polyamide resin represent not more than 50% by weight of the oxypropylation end-product on a statistical basis; and that the preceding provisos be based on complete reaction involving the propylene oxide and the initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the polycarboxy acid for each available hydroxyl radical.

3. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a dicarboxy acid, and (B) high mola1 oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and dimerized higher fatty acids; (b) the molecular weight range of the initial liquid polyamide resin be within 2,500 to 15,000; (c) the molecular weight of the oxypropylation end-product be within the range of 5,000 to 65,000 on an average statistical basis; (at) the oxypropylation end-product be xylene-soluble; (e) the xylene solubility characteristics of the oxypropylation end-product be substantially the result of the oxypropylation step; (f) the initial liquid polyamide resin represent not more than 50% by weight of the oxypropylation end-product on a statistical basis; and. that the preceding provisos be based on complete reaction involving the propylene oxide and the initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the dicarboxy acid for each available hydroxyl radical.

4. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a dicarboxy acid, and (B) high mola1 oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and dimerized higher fatty acids; (b) the molecular weight range of the initial liquid polyamide resin be within 3,000 to 9,000; (c) the molecular Weight of the oxypropylation end-product be within the range of 5,000 to 65,000 onan average statistical basis; (d) the oxypropylatio'n endproduct be xylene-soluble; (e) the xylenesolubility characteristics of the oxypropylation endproduct be substantially the result of the oxypropylation step; (f) the initial liquid polyamide resin represent not more than 50% by weight of the oxypropylation end-product on a statistical basis; and that the preceding provisos be based on complete reaction involving the propylene oxide and the initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the dicarboxy acid for each available hydroxyl radical.

5. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a dicarboxy acid, and (B) high mola1 oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and dimerized higher fatty acids; (b) the molecular weight range of the initial liquid polyamide resin be within 3,000 to 9,000; (c) the molecular weight of the oxypropylation end-product be within the range of 8,000 to 20,000 on an average statistical basis; (d) the oxypropylation end-product be Xylene-soluble; (e) the xylene solubility characteristics of the oxypropylation end-product be substantially the result of the oxypropylation step; (f) the initial liquid polyamide resin represent not more than 50% by weight of the oxypropylation end-product on a statistical basis; and that the preceding provisos be based on complete reaction involving the propylene oxide and the'initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the dicarboxy acid for each available hydroxyl radical.

6. A process for breaking petroleum emulsions of the water-in-oil type characterized by subjecting the emulsion to the action of a demulsifier including acidic fractional esters; said acidic fractional esters being obtained by reaction between (A) a dicarboxy acid, and (13) high mola1 oxypropylation derivatives of liquid polyamide resins; with the proviso that (a) the initial polyamide resin be obtained from an alkylene diamine having not more than 8 carbon atoms and dimerized higher fatty acids; (b) the molecular Weight range of the initial liquid polyamide resin be Within 3,000 to 9,000; (c) the molecular weight of the oxypropylation end-product be within the range of 8,000 to 20,000 on an average statistical basis; (it) the oxypropylation end-product be xylene-soluble; (e) the xylene solubility characteristics of the oxypropylation end-product be substantially the result of the oxypropylation step; (f) the initial liquid polyamide resin represent not more than 50% by weight of the oxypropylation end-product on a statistical basis; and that the preceding provisos be based on complete reaction involving the propylene oxide and the initial liquid resin reactant and with the proviso that the ratio of (A) to (B) be one mole of the dicarboxy acid for each available hydroxyl radical; and that the dicarboxy acid have not more than 8 carbon atoms.

'7. The process of claim 6 wherein the dicarboxy acid is phthalic acid.

2,626,920 19 20 8. The process of claim '6 wherein the dicarboxy REFERENCES CITED midis maleicacid' Th f 11 wn refe ences are f 9. The process of claimfi wherein the dicarboxy file fi s ai r 0 record m the a-cid is succinic acid.

10. The process of claim 6 wherein the dicar- 5 UNITED STATES PATENTS boxy acid is citraconic acid. Number Name Date 11. The process of claim 6 wherein the dicar- 2,454,541 B k at ,1. Nov, 23, 1948 boxy acidis diglycolic acid. N 2,499,365 De Groote et a1. Mar. 7, 1950 S NIELVIN X DE GROOTE. 10

mark

Witnesses to mark:

W. C. ADAMS, I. S. Di: GROOTE. 

1. A PROCESS FOR BREAKING PETROLEUM EMULSIONS OF THE WATER-IN-OIL TYPE CHARACTERIZED BY SUBJECTING THE EMULSION TO THE ACTION OF DEMULSIFIER INCLUDING ACIDIC FRACTIONAL ESTERS; SAID ACIDIC FRACTIONAL ESTERS BEING OBTAINED BY REACTION BETWEEN (A) A POLYCARBOXY ACID, AND (B) HIGH MOLAL OXYPROPYLATION DERIVATIVES OF LIQUID POLYAMIDE RESINS; WITH THE PROVISO THAT (A) THE INITIAL POLYAMIDE RESIN BE OBTAINED FROM AN ALKYLENE DIAMINE HAVING NOT MORE THAN 8 CARBON ATOMS AND HIGHER FATTY ACID POLYMERS OBTAINED BY THE POLYMERIZATION OF UNSATURATED FATTY ACIDS TO A STAGE NOT BEYOND TRIMERIZATION; (B) THE MOLECULAR WEIGHT RANGE OF THE INITIAL LIQUID POLYAMIDE RESIN BE WITHIN 2,500 TO 15,000; (C) THE MOLECULAR WEIGHT OF THE OXYPROPYLATION END-PRODUCT BE WITHIN THE RANGE OF 5,000 TO 65,000 ON AN AVERAGE STATISTICAL BASIS; (D) THE OXYPROPYLATION ENDPRODUCT BE XYLENE-SOLUBLE; (E) THE XYLENE SOLUBILITY CHARACTERISTICS OF THE OXYPROPYLATION ENDPRODUCT BE SUBSTANTIALLY THE RESULT OF THE OXYPROPYLATION STEP; (F) THE INITIAL LIQUID POLYAMIDE RESIN REPRESENT NOT MORE THAN 50% BY WEIGHT OF THE OXYPROPYLATION END-PRODUCT ON A STATISTICAL BASIS; AND THAT THE PRECEDING PROVISOS BE BASED ON COMPLETE REACTION INVOLVING THE PROPYLENE OXIDE AND THE INITIAL LIQUID RESIN REACTANT AND WITH THE PROVISO THAT THE RATIO OF (A) TO (B) BE ONE MOLE OF THE POLYCARBOXY ACID FOR EACH AVAILABLE HYDROXYL RADICAL. 